One theory holds that human beings evolved by running. But humans are slower than either predator…
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It is said that one could wash and shave a Neanderthal, put her in a new set of clothes, and she wouldn't look much different from any other person on the street. Put a Neanderthal in a jogathon, though, and it would be another matter. When it came to running, they had an Achilles' Heel. Literally.

Human heels are short. This causes the Achilles tendon running down the back of the leg to be stretched taut. The tautness of the tendon puts a spring in a person's step, helping them run and keep running. Neanderthals had longer heel bones which took the pressure off the tendon and slowed them down. It may have caused them to be stronger when it came to walking and jumping, but they were not fleet of foot, especially not over long distances. Add to that the fact that Neanderthals were shorter, heavier, and had smaller ear canals so that they might have had trouble with balance, and it makes for a significant cost.

Scientists analyzed the running technique, oxygen efficiency, and heel bone size of a number of different volunteers, and believe that Neanderthals may have expended 11.4 percent more energy on the same run than moderns humans do. If every hunt cost Neanderthals much more than it did humans, early Homo Sapiens would have enjoyed a significant advantage over the other early human competition. Although researchers were careful to say that this difference was not necessarily a contributing factor to the demise of the Neanderthals and the survival of Homo Sapiens. Still, early Homo Sapiens were smaller and weaker than Neanderthals. They needed to have some advantage to get by, and being quick rarely hurts.